Gabriele Rico’s Writing the Natural Way centers on clustering, a technique for quickly making explicit the ideas and associations we have about a topic:
To create a cluster, you begin with a nucleus word, circled, on a fresh page. Now you simply let go and begin to flow with any current of connections that come into your head. Write these down rapidly, each in its own circle, radiating outward from the center in any direction they want to go. Connect each new word or phrase with a line to the preceding circle. When something new and different strikes you, begin again at the central nucleus and radiate outward until those associations are exhausted.
Clustering, like freewriting or writing practice, is another technique I use frequently to move ideas out of my head and onto paper. Often I will “cluster” about a topic, then freewrite based on the cluster I’ve created.